For conventional copper-clad laminates for printed circuit, brominated epoxy resins are primarily used to achieve flame retardant function of the plates via bromine. In recent years, carcinogens, such as dioxin, dibenzofuran and the like, have been detected in combustion products of waste electrical and electronic equipment containing halogens, such as bromide, fluorine, and the like. Moreover, the halogen-containing products may release extremely toxic substance-halogen hydride during combustion. Two Environmental Directives, Waste Electrical and Electronic Equipment Directive and The Restriction of the Use of Certain Hazardous Substances in Electrical and Electronic Equipment, were formally implemented on Jul. 1, 2006. Since the combustion products of halogen-containing products are not environmental and the above Environmental Directives were implemented, the development of halogen-free flame-retardant copper-clad laminates became a hot topic in the industry, and copper-clad laminate manufacturers have launched their own halogen-free flame-retardant copper-clad laminates in succession.
In recent years, with the development of high performance, high functionality and networking of computers and information communication equipment, operating signals tends to be high frequency for high-speed transmission and processing high-capacity information, so as to raise much demand on the materials of circuit boards. Among current materials used for printed circuit base board, epoxy resin having excellent adhesive properties is widely used. However, epoxy resin circuit base board generally has a higher dielectric constant and dielectric loss tangent (the dielectric constant being higher than 4, and the dielectric loss tangent being about 0.02) and has no sufficient high frequency properties, so that it cannot adapt to the demand on high-frequency signal. Thus it is necessary to develop resins having excellent dielectric properties, i.e., having low dielectric constant and dielectric loss tangent. For a long time, those skilled in the art conducted studies on thermosetting polybutadiene or copolymer resin of polybutadiene and styrene having improved dielectric performance.
WO97/38564 discloses a circuit base board prepared by using non-polar tetramer of styrene, butadiene and divinyl benzene added with a magnesium aluminosilicate filler, and glass fabrics as the reinforcing material. Although it has excellent dielectric performance, the base board has a worse thermal resistance, a glass transition temperature of only 100° C., and a very high thermal expansion coefficient, so that it cannot satisfy the requirement on higher temperature (higher than 240° C.) of lead-free process during the manufacture of PCB.
U.S. Pat. No. 5,571,609 discloses a circuit base board prepared by using 1,2-polybutadiene resin or polyisobutadiene having a molecular weight of less than 5000 together with copolymers of butadiene and styrene having high molecular weight, adding a large amount of silica powder as the filler, using glass fabrics as the reinforcing material. Although it has excellent dielectric performance, the addition of ingredients having high molecular weights for improving the adhesive situation of prepregs worsens the processing performance of the process for manufacturing prepregs. Moreover, the manufactured plates have worse rigidity and a very low flexural strength since there is a small proportion of the rigid structural benzene ring in the resin molecules of the whole resin system, and most of the chain segments after crosslinking are composed of methylene having a very low rigidity.
U.S. Pat. No. 6,569,943 discloses using an amine-modified liquid polybutadiene resin having ethylene at the end of molecules, adding a large amount of styrene dibromide monomers having low molecular weight as the curing agent and diluent, dipping glass fabrics to produce a circuit base board. Although the circuit base board has good dielectric performance, the general stacking process of prepregs cannot be used during the pressing molding process since the resin system is in a liquid state at room temperature and cannot be made into non-adhesive prepregs. The technological operation is very difficult.
CN1280337C discloses using a polypolyphenyl ether resin having unsaturated double bonds at the end of the molecules, and using ethylene monomers (e.g., styrene dibromide) as the curing agent. However, these monomers, having low molecular weight, have a low boiling point and will be volatized during the oven-drying process of producing prepregs by dipping glass fabrics, so that the sufficient amount of the curing agent cannot be ensured. In addition, although the reference mentions that polybutadiene resin may be used to modify the viscosity of the system, it does not clearly disclose using polybutadiene resin having polar groups to improve the peel strength.
CN101544841B discloses using a hydrocarbon resin having a molecular weight of less than 11000 and an ethylene content of higher than 60% as the main body, using allyl-modified phenolic resin to improve the tacky properties of prepregs. The peel strength thereof has increased to some extent, but the system has a low thermal resistance after curing. Moreover, the copper-clad laminates have a higher risk of delamination failure during the manufacturing process of PCB.
The system using the hydrocarbon resin as main body has a lower bonding force with metals and has a lower thermal resistance, and will bring a greater chance of loss efficacy risk during the PCB processing process at the downstream of copper-clad plates.